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shyamal_3s
17-07-2010, 06:26 AM
Hi GUY,
Can anybody help me to understand how the TXV setting parameter is decided while HVAC design.

Regards
Shyamal

nike123
17-07-2010, 08:44 AM
Elaborate little more on that! It is not clear about what you are talking here.

Brian_UK
17-07-2010, 11:11 PM
TXV is not set, it is sized according to the design duty of the system, whatever that mat be.

AastroGuru
14-09-2010, 07:45 PM
I guess the setting what you refer is the Superheat. This is set at the manufacturer level and cannot be adjusted once set as per factory settings. The threads at the bottom can be adjusted manually but you will land in some erratic superheat values.

Every system is designed for specific superheat temperature say, 10 deg C and load on the evaporator, say 7 kW. So the TXV setting what you refer will be 2 TON txv with 10 deg superheat.

So its based on evaporator load and amount of superheating you require.

Brian_UK
14-09-2010, 08:38 PM
Seems like another one question wonder who is too impolite to respond. :(

D.D.KORANNE
15-09-2010, 08:30 AM
Tex manufacturer`s catalogue like sporlan,danfoss ,alco will have precise superheat adjustment method/procedure . A tex valve usually does not call for adjustment since factory settings are disturbed or altered by someone .first find out & then resett if requd .

taz24
15-09-2010, 08:43 AM
.

TEV's (TXV's) are nothing more than expensive holes.

They do nothing more than restrict the flow of the refrigerant.

The bigger the hole the more the refrigerant that flows and the
smaller the hole the less refrigerant that flows.

The TEV should be sized to correctly fill the evaporator with the correct
amount of liquid refrigerant. Too much refrigerant and there will be liquid
returning through the suction pipe, too little refrigerant and there will not
be enough to do the work you need.

So sizing the size of the hole is important not the setting.

The setting is used to fine tune any irregularities in specific system set ups.
A correctly sized orifice in a valve will need no setting, they are pre set in the
factory.

A valve can do no more than regulate the superheat temp of the refrigerant
vapour leaving the evaporator. If the superheat temp gets too high compared to
the evaporating temp of the refrigerant (saturation temp) then the valve opens
and if the supeheat temp get too low compared to the evaporating temp, the valve closes.

The valve does not know what it is doing, it just tries to maintain correct superheat
values out of the evaporator.


taz

.

Deniver45
15-09-2010, 10:03 AM
A TXV is determinited by tonnage. TXV's have been around only over 40 years now and are considered extremelly reliable. Actually; where the compressor is the "heart" of a system, the TXV is the "blood pressure", It devides the system into the high and low pressure sides of the system. it is between a low pressure / low temp side and a high pressure / high temp side. In it comes a hot liquid and out comes the cooler saturated vapor. SUPER HEAT COULD NOT BE CREATED WITHOUT A TXV OF SOME SORT, wether it be a TXV or a cap tube. With NO superheat, nothing would cool past the temp of the actual refrigerant in that line. Without superheat; your line temp is the same temp as your refrigerant ( gauge temp )...............kind of like a flooded system where there is a liquid entering the compressor. The TXV is actually one of the most critical parts in the system and I find sensing bulbs on a LOT of TXV's mounted wrong on elbow's and mounted at the 6 ocklock position on the clock rather than 2, 4 8 or the 10 position on the clock.

lana
16-09-2010, 03:54 AM
Hi there,

More or less is said. Sizing a TEV is the first step. Second step is adjusting. The reason is this :
For sizing you need the following data :
1- Capacity
2- Evaporating temperature
3- Pressure drop across the valve
4- Type of refrigerant

Now your compressor at the design condition gives say 20 kW. For calculating the pressure drop across the valve :Pc(condensing pressure )-Pe(evaporating pressure)-P(other pressure drops like distributor,liquid line,drier,...)
The problem is estimating the "other pressure drops". You can only estimate it.
At the end, you come up with say 14bar pressure drop across the valve and you select the orifice according above mentioned data. In the catalogue, say orifice No 04 gives you capacity of 22kW.

NOW : when this orifice is used and every condition is according to the design then, this orifice is 10% bigger than compressor capacity which means you need to adjust it. If you choose an orifice which gives 18kW then again you need to adjust it.
Capacities given in the TEV catalogue can be adjusted something +- 20 to 25 % (according to the model).

If your calculated pressure drops is different than the actual one then, again you will not get the exact capacity from the TEV.

If one knows how to adjust the TEV then it is a relatively simple (but timely) procedure. If one does not know what he/she is doing then it is best NOT to touch it.

Adjusting TEV must be done by measuring super heat out of the evaporator. If superheat is high then open the valve, if superheat is low then close the valve. Measurements must be taken when the system conditions are near design otherwise you will mess up the TEV and life gets unbearable:rolleyes:.

Cheers

chrisft92
20-09-2010, 01:54 PM
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